Existing General Package Radio Service (GPRS)/Universal Mobile Telecommunications System (UMTS) techniques employ network architecture similar to second-generation wireless communication systems, including UMTS Territorial Radio Access Network (UTRAN), GSM/EDGE Radio Access Network (GERAN), Core Network (CN) and Mobile Station (MS), as illustrated in FIG. 1. The GERAN/UTRAN implements all wireless related functions, and the CN handles all voice calls and data connections in GPRS/UMTS and implements switching and routing functions with external networks.
Logically the CN can be divided into a Circuit Switched (CS) domain and a Packet Switched (PS) domain, supporting voice and data services respectively.
The CS domain includes nodes such as Mobile Switching Center (MSC) server, Media Gateway (MGW) and Gateway Mobile Switching Centre (GMSC) server. The MSC server transmits control plane data of the CS domain, and implements functions such as mobility management, call control and authentication encryption; the GMSC server handles call control and mobility control in the control plane for a GMSC; the MGW handles transmission of user plane data.
The PS domain includes nodes such as Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). The GGSN is an interface to interact with external networks. Also, as a user plane anchor (i.e., user plane anchor network element) between a GERAN and a UTRAN, the GGSN transmits data of the user plane. Having a position similar to the MSC server in the CS domain, the SGSN implements functions such as routing forwarding, mobility management, session management and user information storage.
Home Location Registers (HLRs) are used in both the CS domain and the PS domain to store user subscription information.
In existing 3GPP protocols, user plane processing of UMTS is based on a two-tunnel mechanism illustrated as in FIG. 2. In UMTS, the user plane processing is between a Radio Network Controller (RNC, a network element of a UTRAN, used to control wireless resources of the UTRAN) and an SGSN, and between an SGSN and a GGSN, over an Iu interface and a Gn interface respectively. For the two-tunnel mechanism, an SGSN handles both the user plane and the control plane; therefore control plane processing and user plane processing are not separate.
With the introduction of High Speed Packet Access (HSPA) and IP Multimedia Subsystem (IMS), there will be a significant data flow growth in future 3GPP network. At present, in order to improve data processing capability of UMTS, a new UMTS user plane processing mechanism, i.e., direct-tunnel mechanism, has been proposed. As illustrated in FIG. 2, in this mechanism, the user plane processing of UMTS is between an RNC and a GGSN, without an SGSN. For the direct-tunnel mechanism, an SGSN handles functions of the control plane only; therefore control plane processing and user plane processing are separate.
Now with reference to FIGS. 3 to 6, the processes of handover or change between a GERAN and a UTRAN are illustrated hereinafter.
At present, the process of handing over from a GERAN to a UTRAN according to the protocol 43.129 is illustrated as in FIG. 3.
Step S301: a source Base Station Subsystem (BSS) decides to initiate a PS handover.
Step S302: the source BSS sends a PS handover request message to an old SGSN, i.e., 2G SGSN.
Step S303: the 2G SGSN sends a forward relocation request message to a new SGSN, i.e., 3G SGSN.
Step S304: the 3G SGSN builds a relocation request message and sends the message to a target RNC.
Step S305: the target RNC sends a relocation request acknowledge message to the 3G SGSN.
Step S306: the 3G SGSN sends a forward relocation response to the 2G SGSN.
Step S307: the 2G SGSN receives an IP packet from a GGSN and sends the IP packet to an MS via the source BSS.
Step S308: the 2G SGSN forwards the IP packet to the target RNC via the 3G SGSN.
Step S309: the 2G SGSN sends a PS handover request acknowledge message to the source BSS.
Step S310: the MS sends a handover to UTRAN complete message to the target RNC.
Step S311: the target RNC sends a relocation complete message to the 3G SGSN.
Step S312: the 3G SGSN sends an update PDP context request message to the GGSN.
Step S313: the GGSN returns an update PDP context response message to the 3G SGSN.
The process of handing over from a UTRAN to a GERAN is illustrated as in FIG. 4.
Step S401: a source RNC decides to initiate a PS handover.
Step S402: the source RNC sends a relocation request message to an old SGSN, i.e., 3G SGSN.
Step S403: the 3G SGSN sends a forward relocation request message to a new SGSN, i.e., 2G SGSN.
Step S404: the 2G SGSN builds a PS handover request message and sends the message to a target BSS.
Step S405: the target RNC sends a PS handover request acknowledge message to the 2GSGSN.
Step S406: the 2G SGSN sends a forward relocation response message to the 3G SGSN.
Step S407: the 3G SGSN receives an IP packet from a GGSN and sends the IP packet to an MS via the source RNC.
Step S408: the 3G SGSN sends a relocation command message to the source RNC.
Step S409: the source RNC forwards the IP packet to the 3G SGSN, the 3G SGSN forwards the IP packet to the 2G SGSN, and the 2G SGSN forwards the IP packet to the target BSS.
Step S410: the target BSS sends a PS handover complete message to the 2G SGSN.
Step S411: the 2G SGSN sends an update PDP context Request message to the GGSN.
Step 412: the GGSN returns an update PDP context response message to the 2G SGSN.
At present, the process of changing from a GERAN to a UTRAN according to the protocol 23.060 is illustrated as in FIG. 5.
Step S501: an MS decides to perform an inter-system change.
Step S502: the MS sends a routing area update request message to a new SGSN, i.e., 3G SGSN.
Step S503: the 3G SGSN sends an SGSN context request message to an old SGSN, i.e., 2G SGSN, to obtain user context.
Step S504: the 2G SGSN returns an SGSN context response message to the 3G SGSN, and carries the user context information in the context response message.
Step S505: the 3G SGSN sends an SGSN context acknowledge message to the 2G SGSN, informing the 2G SGSN that the 3G SGSN is ready to receive data packets.
Step S506: the 2G SGSN duplicates a buffered data packet and forwards to the 3G SGSN.
Step S507: the 3G SGSN sends an update PDP context request message to a GGSN.
Step S508: the GGSN returns an update PDP context response to the 3G SGSN.
Step S509: the 3G SGSN returns a routing area update accept message to the MS.
Step S510: the MS returns a routing area update complete message to the 3G SGSN.
Step S511: the MS sends a service request message to the 3G SGSN.
Step S512: Radio Access Bearer (RAB) Assignment procedure is performed between the 3G SGSN and an RNC, thereby establishing a RAB.
At present, the process of changing from a UTRAN to a GERAN according to the protocol 23.060 is illustrated as in FIG. 6.
Step S601: an MS decides to perform an inter-system change.
Step S602: the MS sends a routing area update request message to a new SGSN, i.e., 2G SGSN.
Step S603: the 2G SGSN sends an SGSN context request message to an old SGSN, i.e., 3G SGSN, to obtain user context.
Step S604: the 3G SGSN sends an SRNS context request message to a source RNC.
Step S605: the source RNC returns an SRNS context response message to the 3G SGSN, stops sending downlink data to the MS, and buffers the data.
Step S606: the 3G SGSN returns an SGSN context response message to the 2G SGSN, and carries the user context information in the context response message.
Step S607: the 2G SGSN sends an SGSN context acknowledge message to the 3G SGSN, informing the 3G SGSN that the 2G SGSN is ready to receive data packets.
Step S608: the 3G SGSN sends an SRNS data forward command to the source RNC, the source RNC duplicates a buffered data packet and forwards to the 3G SGSN.
Step S609: the 3G SGSN forwards the data packet to the 2G SGSN.
Step S610: the 2G SGSN sends an update PDP context request message to a GGSN.
Step S611: the GGSN returns an update PDP context response to the 2G SGSN;
Step S612: the 2G SGSN returns a routing area update accept message to the MS; and
Step S613: the MS returns a routing area update complete message to the 2G SGSN.
In the processes as illustrated in FIGS. 3 to 6, the user plane data processing when a handover or change from a GERAN to a UTRAN takes place is that, a 3G SGSN forwards data that are forwarded to by a 2G 3GSN to a target RNC; and the user plane data processing when a handover or change from a UTRAN to a GERAN takes places is that, a 3G SGSN forwards data that is forwarded to by a source RNC to a 2G SGSN. However, in a direct-tunnel mechanism where a 3G SGSN no longer performs user plane data processing, data forwarding can not be done via a 3G SGSN. Therefore, the existing data processing method when a handover or change between a GERAN and a UTRAN takes place does not fit the direct-tunnel mechanism.